Safety switch assembly



Nov. 20, 1956 M. BELLIO SAFETY SWITCH ASSEMBLY Filed June 24, 1954 MOTOR l 4 2 a Maw a ww 0 [F I G. 3

United States Patent 2,771,532 'SAFETY SWITCH ASSEMBLY Louis M. Bellio, East Boston, Mass. Application June 24, 1954,-1Serial'No.-439,088 3 Claims. (Cl."200.168)

This invention relates tomewand .usefulimprovements in electrical switch-assemblies andmore particularly to control stations of the pushibutton :type.

Push-button control switches have achieved acceptance for their practical application and long life in controlling electrical-ly powered .mechanical :installations. However, accidents that injure operators and damage machinesare frequently tracedto push-button control stations where the wrong button was accidentally .pushed. Sometimes thlSdS'dLlfiiOtthS operator being'confused by amaze-ora lackof astandard arrangement of buttons. Otherwise, itis oftenzdueto the operatoracting negligently or hastily in-ansemergency.

It has .been'observed that operators are particularly pronetto accidents in thecasewofinstall-ations where inter mittent operation-is zrequiredsfor short periods :of time. Inthe case of 'olfset printing presses,--for example, it is frequentlylnecessaryito intermittently "start and stop the machine for various pperations-such as :washing, cleaning, wiping, adjusting or'inspecting. During'these operations the operators hand is often vextended into .areas that would 'be extremelyrdangerous-if the machine were moving continuously.

To permit the necessary intermittent or jogging operation in such installations, 'the push-button control station is oftenprovided with a Start'button and.Stop"-button, plus auxiliary means which -when-set-will cause the machine to operate only as long-as the start button isdepressed. As soonas 'the start button is released, the machine stops. -B.y repeatedly'depressing the start buttonsfor ashort interval of time, it is ,possible towget the required intermittent or start-stop movement, commonly called inching or fjoggingf However, it is still quite common fortheoperator to forget to sett he auxiliary jogging controlwhen-gradual movement of the machine; is in order, andzthe machine will continue to run after the start button has been=depressed and released. In such situations, the operator is often caught unawares and;physical-injury i-s inflicted-upon him.

Accordingly, it is clear that if push-buttoncontrol stations can be improved to eliminate-this .hazard, a .re-

markable savings .in time, machines, and physical health will result.

Therefore, it is an object ofithisrinvention to provide a push-button control switchassembly having means incorporated-therein that-willa-ssure safe operation of machines controlled thereby.

Another obj-ect is to .provide a control switch assembly wherein a stop switch actuating'buttonisso located with respect to the start buttonthat it will benaturally and automatically depressed -by the operators hand when the start button is depressed unlessthe.operatorconsciously guards against depressingit. 1

Another object is to provide apush-butt-oncontrol station having a switch-actuating plate that is automatically depressed by theoperators palrnorfingers .each.time-the operator places his. thumb on the start button.

Other objects and many of the attendant advantages of 2,771,532 Patented Nov. 20, 11.956

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this invention will be-readily appreciated as the same becomes better understood by reference to the following detaileddescription when-considered in connection with the accompanying drawing wherein:

Fig. '1 is a front view of a switch box assembly with 1 certain parts broken away to show the novel features of this invention;

Fig. v2 is aside view of the-deviceof Fig. l, with the top portion broken away to present a vertical sectional view of the novel features of thisinvention, thesection being taken alongline 2-2 of Fig. 1; and,

.Fig. 3 is a schematic illustrationof an electrical circuit illustrating how the device of Fig. 1 is utilized toieffect control of .a motor.

Referring to Figs. 1 and 2, .1 denotes a conventional switch box .modified according to this invention. The switch box comprises two sections, a body section and a cover section. The body section comprises plates 2, 4, and 6, which form'the rear, top .and bottom walls respectively of the switch box or push button station. Plate 4 is provided with adepending-continuous flange 8 that is recessed or undercut at .10. Bottom plate 6 has a similar flange 12 that is also undercut at 14. Rear plate 2 is provided with holes 16 for receiving screws 13 by which the unit is mounted in place :on a machine or other i structure.

The cover section is U-shaped and comprises plates 29, 22 and.24. Plate 20 forms the front and plates 22 and 24 form the two sides of the switch box. Plates 2! 22 and.24;rest in the undercut portions 10 and 14 of flanges 8 and 12 respectively and are secured in place byscrews with buttons 32 and 34 respectively. Button 32 of start switch 2-8.preferably does not extend beyond front plate 20, as illustrated, so as to help prevent the start buttcn from being accidentally depressed. Start switch 28 is normally open and closes when start button 32 is depressed. Stop switch 30 is normally closed and opens when stop button 34 is depressed. Both "buttons are spring loaded to return totheir normal positions when relieved of manual pressure.

Frontplate 20 has two openings 36 and 38 through which buttons 32 and 34 extend. Collars 40 and 42 are mounted on front plate 20 surrounding openings 36 and 38 and bear suitable legend to designate the functions of these buttons.

Wiring connections are made to the unit through a suitable cable 44 that extends through a hole 46 .inthe bottom plate 6 of the unit. Cable 44 is secured in place by suitable means, e. g. a nut or connector.

The foregoing structure is conventional and comprises part'of thepresent invention. This conventional structure or its equivalent forms the basis of most push button control stations and is commonly .modified to include buttons and switches for actuating conventional circuits for effecting reversal or variations in speed of the'machine with which it is associated. The foregoing structure may also be modified to include conventional auxiliary means for setting the machine for intermittent or jogging operation. Such auxiliary means may take the formof a collar for locking the stop button in depressed position whereby/to keep the stop switch open and 'to limitflow of current to the apparatus controlled thereby through the start button .circuit as explained hereinafter.

However, since the ,present invention .is directed to supplant, although it may include, such auxiliarymeans, the device as illustrated doesrnot include such conventional auxiliary means. :Itis .to be understood however that such auxiliary means for setting the machine for intermittent operation are old and for this reason such means are not illustrated although referred to hereinafter for the purpose of establishing the objects and advantages of the present invention.

It has been observed that when the foregoing conventional switch box assembly is provided with auxiliary control means for placing the machine in condition for intermittent operation, the operator, after setting the auxiliary control means for jogging, automatically rests the palm or fingers of his hand on top of the push button station and customarily employs his thumb to momentarily depress the start button. This is common practice and is a necessary result because (a) the surface of the start button is usually only large enough to accommodate a thumb or a single finger, (b) the push button control station is usually positioned at waist level on the ma chine so as to be within easy reach of the operator, the start button is usually the top button and hence within reach of the thumb when the fingers or palm rest on top of the station, and. (d) the top of the push button unit or station is a comfortable resting place for the operators hand, particularly when the other hand is doing work. Consequently it is possible to provide a safety feature that permits automatic interruption of the motor circuit controlled by a push button station when the operator unconsciously and naturally places the palm or fingers of his hand on top of the push button station, in this way limiting the machine to intermittent operation when the start button is depressed unless the operator consciously avoids contacting the top of the station.

Accordingly the foregoing conventional structure is modified according to the present invention as explained hereinafter to provide this safety feature.

Referring again to Figs. l and 2 there is shown secured to the under side of top plate 4 by means of screws 50 and nuts 52 two mounting brackets 54 spaced from each other by an amount sufficient to receive a micro switch 56 therebetween.

Switch 56 is secured to brackets 54 by means of screws 58 and nuts 59. Switch 56 is a conventional micro switch and is provided with an upstanding sleeve 60 in which is slidably mounted a spring loaded actuating button 62. Sleeve 60 extends through a bushing 64 held in position in a suitable opening in top plate 4 by a nut 66. Bushing 64 acts as a stop for actuating plate 70 hereinafter described.

Pivotally mounted on the upper surface of top plate 4 is a plate 70 provided with a peripheral flange 72 that overlies the top edge of the sides and front of the unit. Plate 70 is secured to a hinge 76 which is affixed to the top of plate 4 at its rear edge by screws 78 and nuts 80, or by other conventional means such as rivets. Switch 56 is similar to stop switch 30 in that it is normally closed. Switch 56 opens when its actuating button 62 is urged downwardly by plate 70 when manual pressure is exerted on the latter. When plate 70 is relieved of manual pressure, it is urged upwardly by the spring loaded button 62. if necessary, plate 70 may also be spring loaded to oppose being urged downwardly by manual pressure.

To eliminate confusion, the electrical connections of switches 28, 30 and 56 are necessarily omitted in Figs. 1 and 2. However, it is to be understood that these switches are provided with conventional terminals whereby they may be interconnected in suitable electrical circuits as in Fig. 3 which schematically shows how the foregoing assembly is utilized in a motor control circuit. The circuit of Fig. 3 is conventional except for the presence of switch 56 in series with switch 30. However, it is to be understood that switch 30 may be eliminated altogether and switch 56 wired directly to common wire 108 as explained hereinafter.

As seen in Fig. 3 switch 56, which in the device illustrated may be considered to be an auxiliary stop switch, is connected in series with stop switch 30. The motor control circuit comprises a 3-.phase power source as represented by lines L1, L2, L3, which supplies current to a 3-phase motor 86 through a conventional 4-pole automatic starter comprising a solenoid 88, armature 90, contact bar 92 carried by armature 90 and four sets of electrical contacts 92 and 94, 96 and 98, 100 and 102, and 104 and 106. Three wires 108, and 112 are used to connect the push button switch box as represented by switches 28, 30 and 56 to the starter. Wire 108 is termed the common lead since it feeds one side of both switches 28 and 30. Wire 110 is the start wire and connects the other side of switch 28 to line L1 through contacts 92 and 96. Wire 112 is the stop wire and connects contact 94 to switches 56 and 30 in series. Contacts 92 and 94 are holding contacts and provide a path for solenoid current when the motor is running. The other three sets of contacts function to supply current to motor 86 when closed by contact bar 92.

It is apparent that switch 30 may be entirely eliminated since switch 56 connected in series therewith is also normally closed and is spring loaded to return to closed position after it has been open and then released. If desired, provision can be made for locking plate 70 in a down position so as to provide an extended jogging operation and to thereby allow the operator to use one finger on the start button when inconvenient to also depress plate 70.

The latching means may be of conventional structure and may comprise, for example, a spring clip pivotally mounted on front plate 20 and adapted in one position to snap over a latch element secured to the forward portion of flange 72 on plate 70. With this arrangement plate 70 may be forced downwardly to cause the spring clip to snap over the latch when the clip has been set in a holding position and to be freely movable up and down when the clip is not set in a clamping position.

Operation of this circuit is as follows: When the start button is momentarily depressed current flows through line L3, contact 104, solenoid 88, start switch 28, start wire 110, contacts 92 and 96 and line L1. Due to the fiow of current through solenoid 88 armature 90 is moved in the direction of the four sets of contacts causing contact bar 92 to close the contacts, whereby current flows to motor 86 from lines L1, L2, and L3 through contacts 96 to 106. Simultaneously current flows between lines L1 and L3 through stop switches 30 and 56, stop wire 112, and contacts 94, 92 and 96 to keep solenoid 88 energized and the contacts closed even after the start switch has reopened. However, as soon as either switch 30 or 56 is opened by manually depressing button 34 or plate 70, the flow of current through solenoid 88 ceases, causing the contacts to be opened and the flow of current to motor 86 to terminate. No more current will flow to motor 86 until the start button is again depressed. If either of switches 30 and 56 are held open, and simultaneously switch 28 is closed, the motor will run only as long as the start button is depressed. If the start button is depressed and then quickly released while switches 30 and 56 are held open the motor will run only an instant and if this is repeated a number of times the motor will run intermittently.

However, while this jogging motion is possible with stop switch 30, the location of stop button 34 with respect to start button 30 is such as to make it difficult to control the circuit in this manner particularly when the operator is accustomed to resting his fingers on the top of the station. The conventional solution to this problem, referred to hereinabove, of providing special auxiliary means to hold the start button 34 depressed, are not satisfactory from a safety standpoint for the reason that it requires a conscious attempt on the part of the operator to set the auxiliary means to hold the stop button in depressed position.

The position of actuating plate 70, however, renders it a simple matter to obtain intermittent motion. This motion, as indicated hereinabove, is automatically obtained when the operator places his hand upon the top of the station, since the weight of his hand causes plate 70 to move downwardly urging button 62 within tube 60 to open switch 56. So long as plate 70 is depressed, switch 56 remains open and current will flow to motor 86 only during the interval of time that start button 32 is depressed. If the operator desires to proceed from an intermittent operation to a continuous operation it is only necessary for him to depress on the start button and to refrain from depressing plate 70. By this arrangement an operator who normally rests his hand on the top of the switch button box will normally achieve intermittent operation when he depresses the start button, and only when he consciously avoids placing his fingers on plate '70 will continuous operation be possible.

The advantage of having plate 70 hinged at the top of the push button station is that a light touch or downward stroke is all that is required to cause switch 56 to open. By having plate 70 of large area as illustrated, the operator is able to find the plate with little difficulty and at the same time his act of resting his fingers on top of the station assures contact with plate 70.

While the invention as illustrated is provided with plate 70 on its upper or top surface, it is pointed out that the plate may be placed along a side wall of the station so that the operator may still continue to use his thumb to depress the start button and allow the plate to be actuated by his fingers which naturally tend to rest on the side wall as they do on the top wall. However, a downward stroke is preferred since it is safer than a stroke in the direction of moving machinery, injuries being more likely when the latter is required.

It is further to be understood that the push button station or switch box may be constructed without top plate 4 and that plate 70 may be directly hinged to the back plate 2 of the unit. In this latter embodiment switch 56 is then held in place by brackets which are secured to the rear plate instead of the top plate due to the fact that the top plate has been omitted. The omission of the top plate will not eifect operation of this unit and at the same time permits the unit to be constructed at lower cost due to the saving in materials.

The illustrated embodiment is preferred when a box already in existence is desired to be modified according to the present invention.

On machines of the multi-station push button type this invention could be used just as described with the added advantage that a man who depresses plate 70 could prevent movement of the machine attempted by other operators at other stations. This could be done by substituting a multi-pole switch for switch 56 and properly wiring the start circuits.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. Therefore, it is to be understood that the invention is not limited in its application to the details of construction and arrangement of parts specifically de scribed and illustrated and that within the scope of the appended claims it may be practiced otherwise than as specifically described or illustrated.

I claim:

1. A switch assembly comprising a switch box defined by front, back, top, bottom and side walls, two switches mounted within said box, one of said switches being normally open and the other of said switches being normally closed, said normally open switch having an actuating button extending through an opening in said front wall, said normally closed switch having a spring-loaded actuating member extending through an opening in said top wall, and a plate hinged to said top wall and overlying said actuating member, said plate when depressed acting to open said normally closed switch, said actuating button and said hinged plate being sufficiently proximate each other to be simultaneously actuated by the thumb and one of the fingers of a human hand.

2. A push-button control station of the type comprising a base plate adapted to be secured to a supporting structure, a cover plate removably secured to the base plate and forming therewith a rectangular enclosure for containing a plurality of switches, said cover plate having a hole, a first normally open switch provided with a pushbutton mounted within said enclosure, said push button extending through said hole in said cover plate and having an operating axis perpendicular to said base plate, a second normally closed switch provided with an actuating button mounted within said enclosure, said actuating button having an operating axis parallel to said cover and base plates and perpendicular to the operating axis of said push button, a plate hinged to said back plate and overlying said actuating button, said hinged plate normally lying in a plane substantially perpendicular to the plane of said base plate, said push button and said hinged plate being sufliciently proximate to each other to be simultaneously actuated by the thumb and one of the fingers of a human hand.

3. A push-button control station comprising a U-shaped base having a back wall, a top wall, and a bottom wall, a U-shaped cover removably secured to said base having a front wall and two parallel side walls, said cover having a hole in its front wall, a first switch secured to said base having a push button extending through the hole in said front wall, said push button having an operating axis perpendicular to said back wall, a second switch secured to said base having an actuating button extending through a hole in said top wall, and a plate hinged to said base and overlying said top wall, said hinged plate resting on said actuating button and acting when depressed to move said actuating button to actuate said second switch, said push button and said hinged plate being sufiiciently close to each other as to be within reach of the thumb and one of the fingers of a human hand so as to permit simultaneous operation of the two switches.

References Cited in the file of this patent UNITED STATES PATENTS 2,307,258 DeSmidt et al Jan. 5, 1943 2,360,818 Turnbull Oct. 17, 1944 2,421,865 Beeman June 10. 1947 

